Die for securing fasteners to sheet material

ABSTRACT

A die for effecting the mounting of a thick metal element to a thinner metal sheet is disclosed wherein by a single stroke of a ram the thick metal element acts as a punch and pierces its own hole in the sheet metal on which it is to be mounted. The thick metal element has one or more laterally extending flanges which abut upon one side of the said sheet, the corners of the element being displaced laterally in the die, preferably under a flange, to clinch the material therebetween. The sheet is also displaced at the displaced region of the element and in the same general direction as the displacd region of the element. The displaced material of the element and sheet is compressed together to form, in effect, a cold weld, but it is not confined laterally, thereby avoiding binding of the displaced material in the back-up die used to displace the material.

United States Patent 1 Grube 1 Oct. 23, 1973 DIE FOR SECURING FASTENERS TO SHEET MATERIAL [75] lnventor: William L. Grube, Lake Bluff, Ill.

[73] Assignee: MacLean-Fog Lock Nut Co.,

Mundelein, Ill.

[22] Filed: Apr. 20, 1972 [21] Appl. No.: 245,710

Related US. Application Data [62] Division of Ser. No. 13,007, Feb. 20, 1970, Pat. No.

UNITED STATES PATENTS 6/l956 Newcomb 29/432 Primary Examiner-James L. Jones, Jr. Assistant ExaminerJ. C. Peters Attorney-James A. Davis et al.

[57] ABSTRACT A die for effecting the mounting of a thick metal element to a thinner metal sheet is disclosed wherein by a single stroke of a ram the thick metal element acts as a punch and pierces its own hole in the sheet metal on which it is to be mounted. The thick metal element has one or more laterally extending flanges which abut upon one side of the said sheet, the corners of the element being displaced laterally in the die, preferably under a flange, to clinch the material therebetween. The sheet is also displaced at the displaced region of the element and in the same general direction as the displacd region of the element. The displaced material of the element and sheet is compressed together to f0rm, in effect, a cold weld, but it is not confined Iaterally, thereby avoiding binding of the displaced material in the back-up die used to displace the material.

4 Claims, 15 Drawing Figures 1 DIE FOR SECURING FASTENERS MATERIAL This application is a division of my co-pending application Ser. No. 13,007 filed Feb. 20, 1970, for Method Of Securing Fasteners To Sheet Material And Resulting Structure and issued on Sept. 26, 1972 as US. Pat. No. 3,693,237.

This invention relates to an improved die for effecting the mounting of a thick metal element to sheet material, and for'purposes of illustration will be described as applied to the mounting pierce nuts to a panel although it is understood that it may be applied as well to securing other devices such as screws, bolts and pins to such sheet metal.

Self-piercing fasteners are understood to be fasteners which are used as punches to form the opening in .sheet metal through which they are to extend and in which they are to be non-rotatively secured. There are at present two general methods for piercing a sheet metal panel with a fastener and securing the piercing fastener to the sheet. The first and most widely used requires that the fastener'be formed adjacent the nose or pilot part first entering the sheet metal, with a portion of the fastenerreduced in cross-sectional area by undercut- TO SHEET ting, grooving or the like. The sheet material adjacent the portion ofreduced area is then forced by a coining, swaging or die forming process, to move laterally into the reduced area to form a lock between the fastener and sheet metal. This method requires a predetermined strength and ductility in the sheet material and a very critical adjustment of the final position-of the mechanism used to'force the metal into the reduced area. Too little force will result in an insufficient movement of the sheet material and a correspondingly weak interlock between the fastener and material, and too much force will weaken the material itself. Furthermore, the for mation of the reduced area in the fastener is difficult to achieve on equipment designed for high volume production of either cold or hot formed fasteners.

The second method does not require a portion of reduced cross-section in the fastener, but requires instead that the pilot of the fastener, i.e., the part of the fastener used as a punch to pierce the sheet material, after is passes through the sheet material, will be deformed to spread over the adjacent material to form the necessary interlock or clinch therewith. Several difficulties are inherent in this method. One of these difficulties is that the deformation can only be accomplished by a step in the back-up die which is contacted by the pilot of the fastener, and the entire pilot is then subjected to compresssion stress. If a relatively large clearance has been used between the periphery of thepilot and the shear edge of the die, most of the compressive stress will 'be dissipated in expanding the pilot into the clearance space, with very little left to deform the pilot over the material itself to form the interlock. With a very weak interlock,'the force required to pull the nut back out of the sheet materialwill be very low and the overall durability of the final structure will be poor. In the majority of instances, there is no interlock at all, the

pilot merely expanding or upsetting in the opening pierced in the sheet material to result in a frictional hold rather than a mechanic! interlock. Another difficulty is that if the die clearance is taken at its maximum, or if the stroke of the tool pushing the pilot thorugh the material is not carefully controlled, the fastener may expand and lodge within the die. There is thus little or no residual space into which the volume of deformed material may flow. Yet another difficulty inherent in this method is that the slugs or pieces of sheet metal cut out by the pilot as it passes through the sheet will tend to lodge or pile up between the step in the back-up die and the pilot of the fastener.

It is the object of this invention to provide a die for forming an interlock between a fastener and a sheet pierced by a pilot portion of the fastener, said die providing ample space for the expansion of displaced material of the pilot used to form the interlock.

A more specific object of this invention is the provision of a die for forming an interlock between a fastener and a sheet pierced by a pilot portion of the fastener, said die including means for deforming specific areas about the periphery of the pilot portion, and deforming portions of the sheet by the deformed portions of the pilot to form said interlock.

Yet another object of this invention is to provide a die for forming an interlock between a fastener having a pilot portion on the end thereof adjacent a laterally extending flange, and a sheet adapted to be pierced by said pilot, said die including means for successively pushing the material of the sheet cut out by the pilot through said die while deforming selected areas of the pilot and adjacent sheet to clinch the sheet between the flange and deformed areas.

These and other objects of this invention will become apparent from the following detailed description of a preferred form of the invention when taken together with the accompanying drawings in which:

FIG. 1 is an exploded plan view in perspective of a fastener and die made in accordance with this invention, the fastener performing the function of a punch relative to a sheet placed over the die;

FIG. 2 is a plan view in perspective of an assembled fastener and sheet;

FIG. 3 is a bottom view in perspective of the assembled fastener and sheet of FIG. 2;

FIGS. 4 and 5 are respectively front and side elevational views of the assembly of FIG. 3;

FIG. 6 is a diagonal elevation in section of the assembly of FIG. 2 taken along line 66 thereof;

FIG. 7 is an enlarged view of a portion of the section of FIG. 6;

FIG. 8 is a fragmentary plan view of the die of FIG.

FIGS.'9 and 10 are elevations in section of the die of FIG. 8, the sections being taken along lines 9-9 and 10' 10, respectively, of 'FIG. 8;

FIGS. 11, l2, l3 and 14 are sections in elevation of the die similar to FIG. 10, showing the progressive steps in the formation of the assembled fastener and sheet;

FIG. 15 is a bottom view of the assembled fastener and sheet.

The invention in general comprises forming the fastener with a lateral abutment which may take the form of a flange extending partly or entirely around the fastener, depending upon the configuration of the fastener. An axially adjacent part of the fastener which does not have the flange is usded as a pilot to be brought down against and through the sheet material to which the fastener is to be secured. The die of this invention is disposed under the material and has an opening to receive the pilot, the opening having a congiguration corresponding to that of the pilot except for small areas which extend into the opening in the path of the pilot. The upper portions of these areas on the die are relieved to form steps having concave, semispherical or dimple-like upper surfaces. The inner edges of these surfaces form gouges which displace the metal in the sides of the pilot. This displaced metal moves down and laterally outward from the pilot along the concave surfaces taking with it adjacent portions of the material of the sheet, which adjacent portions become welded to it and serve to increase the size and strenght of the displaced metal.

Referring now to the drawings for a detailed description of the preferred embodiments depicted therein, there is disclosed in FIGS. 2 and 3 a nut which has been secured to a section of sheet metal 11 by the die of this invention. As shown in FIG. 1, nut 10, for purposes of illustration, has a rectangular section at the upper end of which are formed a pair of oppositely disposed laterally extending flanges 12 and 13. It is understood that nut 10 may have any number of sides, and it may in fact be a cylinder, but in the form selected to illustrate this invention, nut 10 has four sides l4, 15 16 and 17, and flanges 12 and 13 extend laterally from opposite sides 14 and 16. Nut 10 is formed with a threaded opening 18 adapted to receive an externally threaded fastener such as a bolt or'screw. It is contemplated that nut 10 will be non-rotatively secured to sheet 11, said sheet being of metal and comprising a panel or wall of a structure, receptacle or the like. Thus, nut 10 is received in an opening 19 formed in sheet material 11 by the nut itself in a piercing operation hereinafter to be described in detail. Nut 10 therefore fits snugly in opening 19 and is held against rotation relative to sheet 11. It is also restrained against moving out of opening 19 by deformations 20 in both the nut and sheet, said deformations, in accordance with this invention, being formed with a single stroke with the aid of a back-up die 21, the deformations being formed on the side of sheet material 11 opposite that against which flanges 12 and 13 bear. In the form of the invention selected for illustrative purposes herein, the deformations 20 are disposed at the corners of the nut, and take the form, in plan view, of somewhat frustoshperical bosses scooped or gouged out of the corners to leave convave, arcuate groove 22, 23, 24 and 25 in said corners. As shown in FIGS. 4-7 inclusive, each of the bosses is comprised of material 26 originating in nut 10 and material 27 originating in sheet material 11. As shown more clearly in FIG. 7, the material 26 from nut 10 and the material 27 from sheet material 11 is compressed together in an axial direction in a manner to bond the two together to make a substantially integral boss 20.

It may be apparent from the description thus far given that bosses 20 and flanges 12 and 13 clinch sheet material 11 between them to hold nut 10 against axial movement out of opening 19 in sheet material 11.

Referring now to FIGS. 8, 9 and 10, back-up die 21 has an opening 28 which is of the same configuration as the portion of nut 10 below flanges 12 and 13, and of a depth sufficient to give the die the necessary strength to resist deformation under the shear stresses required to pierce sheet material 11. It has been found that a depth equal to approximaterly five thicknesses of sheet material 11 is sufficient for this purpose. Die 21 has an enlarged opening 29 immediately below opening 28 to receive the material punched out of sheet 11 ,by nut 10. Circular depressions 30 are formed in the corners of opening 28, said die 21 having inwardly extending steps 31 at each corner generally completing the circular profile of the depressions 30.

The surface 32 of each depression 30 is concave, semispherical or dimple-like and terminates in a somewhat rounded edge 33 where surface 32 intersects the surface of the inwardly projecting steps 31. The deformations or bosses 20 are formed in the circular depresssions 30 in the following manner;

Referring to FIGS. 11-14, back-up die 21 is shown with the sheet material 11 placed thereon and with a nut 10 placed over sheet 11 in axial alignment with the opening 28 in die 21. The view in FIGS. 11-14 is taken along a diagonal across the opening 28 and is the same view as in FIG. 10. Nut 10 is intended to form its own opening in sheet material 11 and to that end, it is only necessary that the edges 34 at the bottom of nut 10, and forming collectively the periphery of said nut at sheet 11, be reasonably sharp and that the sides 14, 15, 16 and 17 of the nut be parallel with the axis of the nut or perpendicular to the upper surface 35 of sheet material 11. It is assumed in the stage shown in FIG. 11 that several nuts have been previously applied to sheet material with the aid of die 21 so that opening 28 has a number of slugs 36 frictionally retained therein, each slug having been progressively pushed downwardly through opening 28 by the next succeeding slug.

The first stage in the movement of nut 10 into opening 28 in die 21 is shown in FIG. 12. In this stage, the edges 34 of nut 10, acting as shear edges, have partially sheared a slug 37 from sheet 11, the portions of sheet 11 over circular depressions 30 however being merely displaced axially downwardly into said depressions 30. At the stage shown in FIG. 12, slug 37 is in contact at its comers with the rounded edge 33 at the inner ends of steps 31.

The next stage in the movement of nut 10 into opening 28 is shown in FIG. 13, and at this stage the bottom surface 38 of nut 10 has contacted the rounded edges 33 and the material of sheet 10 which was disposed over depressions 30 has been displaced downwardly and laterally outwardly into said depressions 30.

The amount of material from sheet 11 displaced into the depressions 30, however, is not sufficient to fill said depressions; It may be noted that the completed slug 37 has now pushed a preceding slug 36 into the clearance opening 29 and that the lowermost slug 36 is substantially half way out of the opening 28.

The final stage in the movement of nut 10 into opening 28 is shown in FIG. 14. In this stage, the edges 33 at the inner ends of concave surfaces 32 have now cut into the corners of bottom surface 38 on nut 10, and, because of the concave nature of said surfaces 32, the material in the corners of nut 10 has been displaced laterally outwardly against the previously displaced material of sheet 11 in these depressions 30 to continue the movement of said displaced sheet material into the depressions 30. It may be noted that even the bottom of the stroke of nut 10, the depressions 30 still are not completely filled, so that there is no binding effect created between the nut and die by virtue of the displaced material. The material of sheet 11 displaced by nut 10 into depressions 30 is shown at 39 in FIGS. 13 and 14 and the material of nut 10 displaced by the die is shown at 40 in FIG. 14. As shown in FIG. 13, the material from the nut is forced upon concave surface 32 and compressed against and partly under the previously displaced material 39 from sheet 11. The pressure is sufficient to form an integral boss 20 wherein the material from both the nut and the sheet have, in effect, been cold welded together. The movement of nut to its final stage in opening 28 has caused the lowermost plug 36 to be ejected into the clearance space 29 in die 21. Sheet 11 may now be lifted off die 21, and nut 10 will be firmly clinched upon sheet 11 by the flanges 12 and 13 on the one side and the bosses on the other.

Since nut 10 acts asa punch to shear slugs 36 from sheet 11, it must be'of sufficient thickness to withstand the compressive force exerted thereupon during the piercing operation without exceeding its maximum compression strength.

Depressions 30 are shown generally circular in outline. They may have any other shape desired, the circular form being the simplest and most economical to make. Similarly, the inwardly projecting steps 31 need not be a continuation of the contour of the depressions 30 but they need only to be so related to the depressions that the volume of material displaced from the sheet 11 and nut 10 will not exceed the volume of the space in said depression 30. The center of the concave surface of each depression is preferably located approximately under a corner of a nut, as shown in FIG. 15.

Opening 28 in die 21 and the inwardly projecting steps 31 can readily be formed in a single operation by the use of a breach. Depressions 30 can be formed equally as readily with the use of an appropriately shaped end mill.

It may be noted in FIG. 12 that nut 10 has moved approximately one-half the thickness of material 11 toward die 21, and it may be taken as one of the criteria for the design of the die 21 that in the FIG. 12 stage the nut will move one-half the thickness of the material toward die 21 so that the material 11 will be definitely sheared by the die 21 around the periphery of the opening between depressions 30. At the depressions, however, the material disposed above said depressions is extruded, rather than sheared, so that whatever material enters the depressions is still a part of sheet 1 1. The ductility of the material of sheet 11, however, will have some effect upon the location of the end of the shear and the commencement of the extrusion of the material. Generally, this commencement of the extrusion process will occur where the straight edge of the opening 28 intersects therounded edge 33, but it is possible that once shear has been propagated in a very brittle sheet material, it may well continue along the shear edge into the depressions 30 where it terminates against the shear propagated at right angles from the adjacent edge. However, complete shearing of the material in depressions 30 will not affect the suffessful formation of the bosses 20, since the compressive stresses imposed upon the material in the bosses causes the material to reunite with the sheet at the end of the stroke of nut 10.

Although a line of demarcation has been shown in the drawings between the material of the sheet 11 and the material of nut 10 in depressions 30, actually, in the final structure, this line cannot be seen, since the two materials have been compressed together by the die and nut and have become bonded together.

Thus by a single stroke of a punch, nut 10 has pierced an opeing in sheet 11 and has been clinched to the sheet on both sides of the opening. A stronger clinching action has been achieved so that the nut will resist a greater axial pull while at the same time avoiding any binding effect of the clinched nut in the back-up die.

Since the threaded opening in the above-mentioned fastener 10 is not utilized in the die of this invention, it may be apparent that the said die may be used to secure the heads of screws or bolts to a sheet or panel, or to secure pins or shafts to a panel when such pins or shafts are provided with an appropriate head.

Thus it is understood that this invention is not limited in its scope to the die and resulting structure hereinabove described, but its scope is to be determined instead by the appended claims:

I claim:

1. A die for effecting the mounting on a relatively thin metal sheet of a metal element having a pilot portion of predetermined polygonal section and size and thicker than said metal sheet with mounting flanges projecting laterally from the top end region of the pilot portion, said die having an opening therein of a sectional shape and size conforming to said predetermined polygonal section and size of the pilot portion of the metal element except for protuberances of an arcuate sectional shape which project inwardly of the die opening atpositions spaced peripherally of the opening, said die having recesses therein which have axes parallel to the axis of the die opening and which are each conventric with one of said arcuate protuberances, said recesses each being of a diameter corresponding generally to that of the adjacent arcuate protuberance, and said recesses each having a bottom surface merging with the top surface of the adjacent protuberance to define a unitary dimple-type depression.

2. A die for effecting the mounting on a relatively thin metal sheet of a metal element having at one end region thereof a pilot portion of constant cross section and size and of a length greater than the thickness of the metal sheet with an abutment extending laterally of the element adjacent the pilot portion, said die having an opening therein of a sectional shape and size conforming to said constant cross section and size of the metal element, except for protuberances which project inwardly of the die opening at positions spaced peripherally of the opening and presenting transverse surfaces to the metal element, said die having recesses adjacent each protuberance the bottom surfaces of which recesses are extensions of the surfaces on the protuberances and together with said protuberance surface form unitary concave surfaces of round peripheral shape.

3. A die as defined in claim 2, said pilot portion cross section being polygonal, and wherein said protuberances are located at peripheral positions of the die opening corresponding to the corners of the polygonal cross section of the pilot portion.

4. A die as defined in claim 2, the cross section of the metal element being a regular polygon having flat sides intersecting to form corners, and the center of each round peripheral surface on the die being disposed substantially under a corner of the metal element.

: UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,628 Dated Octoocr 23, 1973 Inventor(s) William L. Grube It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page 73? "Assignee: l-iacLean-Fog Lock Nut 00.

should read Assignee': MacLean-Foggg Lock Nut Co.

Column 1, line 11, after "mounting" insert of line M5, "is" should read it line an, "mechanicl" should read mechanical Column 2, line L l, "Fig. 3" should read Fig. 2

line 62, "usded" should read used line vb, "congiguration" should read configuration Column 3, line all, "groove" should read grooves Column L line 58, after "even" insert at Column 6, claim 2, line 52, "surface" should read surfaces Signed and sealed this 30th day of April 1971+.

( DEAL Autest' EDWARD MELETCEHEILJR. V I C. MARSHALL DANN Attesting Officer I 1 Commissioner of Patents FORM PO-105O (10-69) V USCOMMDC 603w", I Y U. 5. GOVERNMENT PRINTINQ QFfIC! 199 O36G-!3 4 

1. A die for effecting the mounting on a relatively thin metal sheet of a metal element having a pilot portion of predetermined polygonal section and size and thicker than said metal sheet with mounting flanges projecting laterally from the top end region of the pilot portion, said die having an opening therein of a sectional shape and size conforming to said predetermined polygonal section and size of the pilot portion of the metal element except foR protuberances of an arcuate sectional shape which project inwardly of the die opening at positions spaced peripherally of the opening, said die having recesses therein which have axes parallel to the axis of the die opening and which are each concentric with one of said arcuate protuberances, said recesses each being of a diameter corresponding generally to that of the adjacent arcuate protuberance, and said recesses each having a bottom surface merging with the top surface of the adjacent protuberance to define a unitary dimple-type depression.
 2. A die for effecting the mounting on a relatively thin metal sheet of a metal element having at one end region thereof a pilot portion of constant cross section and size and of a length greater than the thickness of the metal sheet with an abutment extending laterally of the element adjacent the pilot portion, said die having an opening therein of a sectional shape and size conforming to said constant cross section and size of the metal element, except for protuberances which project inwardly of the die opening at positions spaced peripherally of the opening and presenting transverse surfaces to the metal element, said die having recesses adjacent each protuberance the bottom surfaces of which recesses are extensions of the surfaces on the protuberances and together with said protuberance surfaces form unitary concave surfaces of round peripheral shape.
 3. A die as defined in claim 2, said pilot portion cross section being polygonal, and wherein said protuberances are located at peripheral positions of the die opening corresponding to the corners of the polygonal cross section of the pilot portion.
 4. A die as defined in claim 2, the cross section of the metal element being a regular polygon having flat sides intersecting to form corners, and the center of each round peripheral surface on the die being disposed substantially under a corner of the metal element. 